1. Field
This application relates generally to communications and, in some aspects, to calibrating a delay line.
2. Background
A delay line provides a mechanism to impart a known delay on a signal. For example, a signal input into a delay line may exit the delay line relatively intact after a specified period of time. A typical use of a delay line involves delaying a clock signal to provide a clock signal with a different phase. Another typical use of a delay line involves delaying a signal in a circuit to align information in that signal (e.g., clock edges or data) with information in other signals. Another potential use relates to delays in ultra-wideband transmitted reference transmitters and receivers. For a transmitter, a given delay may be provided between a reference pulse and data pulse. For a receiver, that same delay may be imparted on a reference pulse to correlate the reference pulse with a data pulse. A delay line also may be used in a ring oscillator for clock generation, such as an inverter chain-based delay line. A delay line also may be used for a super regenerative receiver with a delay feedback through a gain element. Many other uses are possible.
In practice, the actual delay of a delay line may vary from its nominal, intended value. For example, factors such as integrated circuit process variations and temperature may cause the actual delay of the delay line to be higher or lower than the nominal value. The impact on the delay of the delay line due to integrated circuit process variations is relatively static. That is, once the delay line is manufactured, the actual delay of the delay line may be a specific value that is slightly below or above the nominal value. The impact on the delay of the delay line due to temperature variation may be relatively dynamic. Here, the delay may deviate over time in response to changes in temperature in the operating environment.
Accordingly, applications that require a relatively precise delay may incorporate some form of delay line calibration. For example, the delay of a tunable delay line may be varied based on the value of a control signal provided to the delay line. In this case, a control mechanism may be used to adjust the delay of the delay line to maintain the delay with a given range of values (e.g., a within certain percentage of the nominal delay). Here, provisions may be made to measure or estimate the current delay of the delay line. If this measurement or estimate indicates that the delay is not within the desired range of values, the control signal may be used to adjust the delay of the delay line back to an acceptable value.